Inhibitors for prolonging corrosion protection of Mg-rich primer on Al alloy 2024-T3

Abstract

This research investigated the possibility of adding inhibitors into magnesium-rich primer (MgRP) to prolong the corrosion protection time of MgRP on Al alloy 2024-T3. Three inhibitors: sodium benzoate (SB), sodium dodecylbenzenesulfonate (SDBS), and 8-hydroxyquinoline (HQ), were tested and added into MgRPs separately. Potentiodynamic scans on pellet electrodes confirmed that the inhibitors reduced Mg corrosion rate. The coating systems with and without inhibitors were compared through electrochemical tests, hydrogen volume measurement, accelerated weathering tests, and adhesion tests. It was observed that the addition of SB, SDBS, and HQ into MgRPs could prolong cathodic protection time and improved barrier properties of MgRPs, without compromising adhesion strength.

Appendix

The moles of hydrogen generated from MgRP ($n_{{{\text{H}}_{2} }}$) can be calculated using the ideal gas law. The moles of Mg consumed ($n_{\text{Mg}}$) can be calculated using equation (1):

$$n_{\text{Mg}} = n_{{{\text{H}}_{2} }} = \frac{{pV_{{{\text{H}}_{2} }} }}{\text{RT}}$$

(1)

where $p$ is the atmospheric pressure, $V_{{{\text{H}}_{2} }}$ is the volume of H₂ collected, R is the ideal gas constant (0.0826 L atm mol⁻¹ K⁻¹), and T is the temperature.

Total moles of Mg in an MgRP ($N_{\text{Mg}}$) can be calculated using equation (2):

$$N_{\text{Mg}} = \frac{{{\text{Mass}}_{\text{Mg}} }}{{M_{\text{Mg}} }} = \frac{{{\text{PVC}} \times T \times A \times D_{\text{Mg}} }}{{M_{\text{Mg}} }}$$

(2)

where ${\text{Mass}}_{\text{Mg}}$ is the total mass of Mg pigments in a MgRP, $M_{\text{Mg}}$ is the molar mass of Mg (24 g/mol), PVC is the pigment volume concentration of the MgRP, T is the thickness of the MgRP film, A is the exposed area of the MgRP, and $D_{\text{Mg}}$ is the density of Mg pigments (1.738 g/cm³).